This invention relates to a method and an apparatus for drying wood which are particularly suited for boxed heart lumber (lumber with heart center), which is used in houses as pillars, etc.
For use as a constructional material as pillars, etc., wood must be dried to reduce its moisture content to a certain level to prevent deformation or cracking on shrinkage. In particular, constructional wood recently tends to be supplied in pre-cut or pre-worked form, and dried wood with higher dimensional stability and less susceptibility to cracking has been demanded.
A wood drying method comprising softening wood by initial steaming at 95xc2x0 C. for 8 hours followed by drying at a dry-bulb temperature of 120xc2x0 C. and a wet-bulb temperature of 90xc2x0 C. for 72 hours has been proposed as a technique for achieving drying in a short time while suppressing cracking on the surface (surface checks) (see Abstract of the 49th Convention of The Japan Society of Wood).
When the proposed method was applied to boxed heart lumber of Japan cedar (11.5 mmxc3x971.5 mmxc3x973000 mm), however, all of 70 test pieces of the wood suffered from cracks in the internal portion, and darkening (scorching associated with high-temperature drying) of the wood color was observed. We heretofore have no drying method and apparatus that satisfy the requirements: (1) causing no surface checks, (2) suppressing darkening, and (3) causing no internal cracks. It has therefore been keenly demanded to develop a method and an apparatus satisfying all these requirements.
An object of the present invention is to provide a method and an apparatus for drying wood which suppress surface checks, internal cracks, and darkening of wood.
The above object of the present invention is accomplished by a method of drying wood comprising drying wood in a drying chamber at a controlled temperature and a controlled humidity, wherein the temperature and the moisture content inside the wood while dried are monitored continuously or intermittently, and the temperature and the humidity in the drying chamber are controlled based on the resulting data.
The object of the invention is also accomplished by an apparatus having a drying chamber in which wood is to be placed and dried and of which the temperature and the humidity are controllable, which is equipped with a means for measuring the temperature inside the wood while dried and a means for measuring the moisture content inside the wood while dried.